The present invention relates to a fan wheel for electrical machines, in particular alternators of motor vehicles.
The present invention relates to a fan wheel for electrical machines, in particular alternators of motor vehicles, according to the general class of claim 1.
Fan wheels are typically used to cool electrical machines, in particular alternators in motor vehicles, the fan wheels having rigid fan blades and being dimensioned such that they deliver enough cooling air, even at low rotational speeds, to dissipate the heat from power losses occurring in the electrical machine. In the case of fan wheels with rigid blades, the quantity of air conveyed increases as rotational speed increases. Since, starting at a certain rotational speed, the heat from power losses from generators in motor vehicles does not increase as drastically as it does in the lower rotational speed range, more air is conveyed by the fan wheel at higher rotational speeds that would be required to dissipate the heat from power losses. The quantity of cooling air conveyed creates disturbing sounds, particularly at higher rotational speeds. Furthermore, additional power is required from the internal combustion engine of the motor vehicle to drive the fan wheel to convey the cooling air at an unnecessarily high rate in the upper speed range.
It is known from DE-OS 20 49 679 that, to taper off the quantity of cooling air conveyed at higher rotational speeds, all of the fan blades of a fan wheel are configured such that each one is connected with a fan disk in a fixed manner only via its radially outward end section. The inner section of each fan blade is a flexible tab that is swiveled radially increasingly outwardly by a centrifugal force occurring there as rotational speeds increase. As a result, the cross section of the air channels formed by the adjacent fan blades is reduced, through which said air channels the cooling air below the fan blades that is drawn in axially is blown radially outwardly. With this means of attaining the object of the invention, although the drive power for the fan wheel is reduced as rotational speed increases and, thereby, the overall efficiency of the machine is improved, the fan blades are tilted forward from the inside to the outside in the direction of rotation such that higher pressure also builds on the flexible, outwardly swivelable tabs as rotational speed increases. Since the inwardly directed, swivelable ends of the fan blades also extend freely into the air channels at high rotational speeds, the disturbing fan noise is further increased as a result. In addition, blade oscillations occur there when the drive speed of the fan wheel fluctuates, the blade oscillations being capable of generating additional noises and resulting in material fatigue, in particular, and, therefore, to the fan blades breaking off.
With the present means of attaining the object of the invention, the aim is not only to reduce the drive power at the fan wheel at high rotational speeds, but also to markedly reduce the disturbing noises occurring there and to thereby simultaneously improve the oscillatory behavior of the fan blades.